At the approximate fractional gradient point actually. Think about it. What is ΔX for the contrast parameters outlined in the ISO film speed standard? 0.29 logs. Hm is Δ1.0 logs from the metered exposure point. And the average log-H range below the metered exposure point is Δ1.28 log-H. 1.28 - 1.00 = 0.28 logs. This is not a coincidence.

Last edited by Stephen Benskin; 05-11-2013 at 11:05 PM. Click to view previous post history.